[noise] psk in Noise explorer

[Justin Cormack]

Looking at KNpsk0 in Noise Explorer, the first message which is "psk, e" says

"Message contents benefit from message secrecy and some forward
secrecy: the compromise of the responder's long-term private keys,
even at a later date, will lead to message contents being decrypted by
the attacker."

There isn't any forward secrecy in this message at all I don't think,
so this seems a bit off to me.

Also, it would be really nice if the wording could distinguish the psk
keys and the private keys, as the "long-term private keys" above is
actually referring to the psk, which is not a private key, and also
could well have different lifecycle to the asymmetric keys, for
example if it is a resumption key, and also unlike the private key is
distributed to multiple parties, so is more likely to leak so calling
out which key is being referred to would be helpful.

Justin